1. Field of the Invention
This description relates to a new system and topology for providing cellular service in multiple bands by using a cable TV network. The system can improve the in-building coverage and the total available capacity of different cellular networks, using the same CATV network. These cellular networks may have multiple air interfaces, different frequency bands and may be operated, simultaneously, by different cellular service providers. As used herein, the terms “mobile”, “cellular”, and “wireless” are meant generically to refer to radio systems or networks such as UMTS, GSM900, GSM1800, PCS1900, TDMA800, CDMA800, CDMA2000 1X/3X, or PDC. Other types are known, and still other types may be hereafter developed, and it will be appreciated that “mobile”, “cellular”, and “wireless” are terms intended to include all such systems.
In particular, this description relates to an extension to conventional mobile radio networks using cable TV or HFC (Hybrid Fiber Coax) networks (and the like, all referred to generally as CATV networks, hereafter). To be even more specific, there is described an approach to merging CATV networks into mobile radio networks to provide improved voice & data services and coverage, while enhancing network capacity; to providing in-building access for any combination of mobile radio terminals, in a mobile radio network; to combining and carrying any combination of mobile radio signals on the CATV system, without interfering with each other, or the CATV service.
2. Related Work
The basic theory by which mobile radio and cellular networks operate is well known. Geographically distributed network access points, each defining cells of the network, characterize cellular radio networks. The geographically distributed network access points are typically referred to as base stations BS or base transceiver stations BTS, and includes transmission and reception equipment for transmitting signals to and receiving signals from mobile radio terminals (MT). Here, a MT includes not only a normal cellular phone, but any device capable of performing cellular communications. Each cell (or sector) is using only part of the total spectrum resources licensed to the network operator, but the same capacity resources (either frequency or code), may be used many times in different cells, as long as the cell to cell interference is kept to a well defined level. This practice is known as the network reuse factor. The cells may be subdivided further, thus defining microcells. Each such microcell provides cellular coverage to a defined (and usually small) area. Microcells are usually limited in terms of their total available capacity.
One problem needing to be solved is the inability of present frequency or code reuse techniques (sectorization and cell-area subdivision) to deal with the “third dimension” problem. Cellular networks have no means to deal with the problem of user terminals at higher-than-usual elevations, e.g. upper floors of high-rise office or residential buildings. The overall demand for mobile services has caused cellular network operators to develop an intensive network of BTSs in urban areas. This has improved spectrum utilization (increased network capacity) at ground level, but has aggravated the problem in high-rise buildings where MTs now ‘see’ several BTSs on the same frequency or code.
Cells in a cellular radio network are typically connected to a higher-level entity, which may be referred to as a mobile switching center (MSC), which provides certain control and switching functions for all the BTSs connected to it. The MSCs are connected to each other, and also to the public switched telephone network (PSTN), or may themselves have such a PSTN interface.
The conventional implementation of mobile radio networks has had some important limitations. When operating above 1 GHz, it is necessary in a conventional mobile radio network to build numerous base stations to provide the necessary geographic coverage and to supply enough capacity for high-speed data applications. The base stations require an important amount of real estate, and are very unsightly.
Another limitation is that, since cellular towers are expensive, and require real estate, it is economically feasible to include in a network only a limited number of them. Accordingly, the size of cells might be quite large, and it is therefore necessary to equip the mobile radio terminals with the ability to radiate at high power so as to transmit radio signals strong enough for the geographically dispersed cellular towers to receive.
As the cell radius becomes larger, the average effective data rate per user in most packet based protocols decreases accordingly and the high-speed data service might deteriorate.
Yet another limitation to cellular radio networks as conventionally implemented is that the cellular antennas are typically located outside of buildings, even though it would be highly beneficial to provide cellular service inside buildings. The penetration of cellular signals for in-building applications requires high power sites, or additional sites or repeaters to overcome the attenuation inherent with in-building penetration. As frequency increases, the in-building signal level decreases accordingly. Because the base station antennas are located outside of buildings, it is difficult for mobile radio terminals to transmit signals strong enough to propagate effectively from inside of the building to outside of the building. Therefore, the use of mobile terminals inside buildings results in reduced data rate and consumes a substantial amount of the limited battery time.
Yet another limitation of mobile radio networks as conventionally implemented is the inherent limited capacity of each and every BTS to provide voice and data service. This capacity shortage is due to the way the spectrum resources are allocated to each BTS. To provide for reasonable voice and data quality, each BTS can use only a part of the total spectrum resources owned by the cellular operator. Other BTSs can reuse the same part of the spectrum resources as a given BTS, but a pattern of geographic dispersion has to be respected. This is called a code reuse factor for CDMA based technologies, and frequency reuse factor for TDMA based technologies.
Because CATV is so ubiquitous today, even in rural areas, it becomes very interesting to attempt to overcome the above identified limitations of cellular systems by taking advantage of the bandwidth of the CATV networks.
FIG. 1 shows a CATV system, in highly simplified schematic form. In the CATV system, the CATV head end is connected to a CATV cable network. The CATV cable network includes various equipment, such as amplifiers. Most CATV networks today are bidirectional. That is to say, communications from the CATV head end toward the end user (i.e., downstream communications) and also communications from the end user to the CATV head end (i.e., upstream communications) are possible.
The CATV network shown in FIG. 1 is a bidirectional system. The CATV amplifiers are bidirectional as well. Upstream communications are carried in a relatively narrow band of 5-45 MHz. Downstream communications are carried in a relatively wide band of 50-750 MHz or 50-860 MHz, depending on the particular system.
The communications traveling downstream from the CATV head end are passed on through a tree-shaped network to a set-top box (STB). The STB connects to the television set. Of course, it is quite possible that the television set includes the appropriate equipment to allow the connection of the cable without the use of a STB. Likewise, there might be a cable modem or other related device. For convenience, herein, STB is used to mean any devices of this kind.
FIG. 2 shows a conventional approach to carrying bidirectional cellular communications over such a network. In this approach, the public land mobile network (PLMN) is connected to the cable system via an interface I/F. Downlink communications from the PLMN are carried through the CATV amplifiers, and the CATV network through a remote antenna driver (RAD). The RAD takes the downlink communications and broadcasts them to an MT.
Upstream communications from the mobile terminal travel through the RAD, and through the upstream portion of the bandwidth, through the CATS amplifiers, through the I/F, and then to the PLMN. Naturally, frequency conversion is necessary at the RAD so that the uplink communications can be put into the upstream bandwidth of the CATV network.
The prior approaches for carrying wireless signals over the CATS network include re-arranging or re-packaging the original radio signal to fit into the existing CATV standard frequencies (5-45 MHz and 50-750/860 MHz) and channels. This is typically done by active elements, which up- and down-convert the wireless frequencies to match the known standard CATV operational frequencies in the standard CATS upstream and downstream frequencies. Using the standard CATV channels, however, reduces the available bandwidth of the CATV operators in providing video, data and voice according the common CATV standards like DOCSIS and DVB.
Such approaches have all been disadvantageous, however. In particular, if one wishes to re-arrange and re-pack the full UMTS frequency band (1920-1980 MHz, 2110-2170 MHz) into the standard CATV channels, one finds that the UMTS uplink bandwidth (60 MHz) is too large, and hence impossible for the CATV upstream (40 MHz) to carry. Even if a smaller UMTS bandwidth were to be carried over the CATV upstream, this would dramatically reduce the scarce upstream CATV resource. Some patent documents representing such disadvantageous approaches are now summarized.
U.S. Pat. Nos. 5,802,173 and 5,809,395 (related patents) describe a radiotelephony system in which cellular signals are carried over a CATV network. However, uplink cellular communications are frequency converted to “in the range 5 to 30 MHz”. Such a conversion is necessary because the CATV network is normally frequency-divided into two bands: a high band which handles downstream transmission (head-end to hub to subscriber) and a low band which handles upstream transmission (subscriber to hum to head end). In other words, any upstream signals or communications over about 45 MHz are filtered out by the CATV network itself as a part of the normal operation of the network. Under the '173 approach, upstream communications all must be fit into the low Sand (i.e., in “a portion of the frequency spectrum allocated in the CATV system for upstream communications”).
U.S. Pat. No. 5,828,946 describes a CATV based wireless communications scheme. Under the '946 approach, to avoid multiple outdoor cellular receptions from causing noise over the CATV network, only the signals received at a sufficient power level are converted and sent upstream.
U.S. Pat. No. 5,822,678 acknowledges that the frequency-divided nature of CATV networks is a problem. In particular, the '678 patent teaches that the limited bandwidth available “within the frequency band of five megahertz to 40 megahertz” poses “a problem with using the cable plant to carry telephonic signals.” To solve this problem, the '678 approach is that “currently existing frequency allocations for cable television are redefined.” That is to say, the division between high and low bands in a CATV network is moved from about 40 MHz to several hundred megahertz higher. This simplistic approach is highly disadvantageous because it requires replacement of substantial amounts of equipment in any CATS network. Such an expensive approach has not yet been adopted for actual use.
U.S. Pat. No. 5,638,422, like the previously mentioned documents, teaches carrying uplink cellular communications in “the return path of the CATV system, i.e. 5 to 30 MHz, for telephone traffic in the return direction.” Furthermore, downlink cellular communications are disadvantageously carried in “the forward spectrum, i.e. 50 to 550 MHz of the CATS system”. This interferes with CATV signals, and is problematic for the CATV operator, who must move existing programming to other parts of the spectrum to make room for downlink cellular signals.
U.S. Pat. No. 6,223,021 teaches how to use programmable remote antenna drivers to provide augmented cellular coverage in outdoor areas. For example, during morning rush hour, the remote antennas are tuned to one frequency set and to another during evening rush hour. Thus, outdoor communications can be flexibly augmented. The remote antenna drivers and their antennas are hung from outdoor CATV cables. The '021 patent does not describe how to solve the problem of limited upstream bandwidth for uplink cellular communications.
U.S. Pat. No. 6,192,216 describes how to use a gain tone from remote antenna locations, sent over a CATV network, to determine a proper level of signal at which each remote antenna location should transmit.
U.S. Pat. No. 6,122,529 describes the use of outdoor remote antennas and remote antenna drivers to augment an existing cellular coverage area, but only in areas where outdoor cellular antennas provide no coverage. The signal of a given BTS sent to a cellular antenna tower is simulcast over the remote antennas to overcome “blind” areas.
U.S. Pat. No. 5,953,670 describes how to use remote antenna drivers as well, but adopts the above-identified approach of sending uplink cellular communications in the low CATV band.